1. Field of the Invention
The present invention relates to an exhaust control system for a cylinder fuel injection engine. More particularly, the invention relates to an exhaust control system realizing early activation of a catalytic converter.
2. Description of the Related Art
In general, an exhaust gas of an engine is purified by a catalytic converter. When the catalytic converter is not activated, such as upon starting up of the engine, the exhaust gas is discharged to the atmosphere with little purification. Therefore, in Japanese Patent Application Laid-Open No. 11-294220, as a method for preventing fatigue and decomposition of catalytic converter, quickening purification of exhaust gas, appropriately heating the catalytic converter and prevention of discharge of unburnt gas, it has been disclosed a fuel injection control system in a cylinder direct injection type internal combustion engine directly injecting a fuel by fuel injection valve which includes engine start-up detecting means for detecting start-up of the internal combustion engine, temperature detecting means for detecting a temperature of the internal combustion engine, cold engine condition detecting means for comparing a detection value obtained by the temperature detecting means and a preliminarily stored predetermined value for detecting a low temperature condition of the engine from the result of comparison, and control means for limiting fuel injection in an expansion stroke or an exhaust stroke only during a predetermined period (predetermined engine revolution cycles) from initiation of injection when starting up of the internal combustion engine is detected and cold engine condition is detected by the cold engine condition detection means. On the other hand, in Japanese Patent Application Laid-Open No. 11-311139, as a method for realizing quick activation of catalytic converter by interrupting fuel supply for a part of cylinders upon starting-up of a multiple cylinder engine, it has been disclosed an air/fuel ratio control system for a multi-cylinder internal combustion engine which includes a catalytic converter for purification of exhaust gas arranged in an exhaust passage of the internal combustion engine having a plurality of cylinders, air/fuel ratio control means for starting up for controlling air/fuel ratio for rich mixture operation in part of cylinders among a plurality of cylinders and lean mixture operation in remaining cylinders upon cold start of the internal combustion engine, wherein catalytic converter temperature detecting means for detecting a temperature of the catalytic converter for setting air/fuel ratio until the catalytic converter temperature detected by the catalytic converter temperature detecting means reaches a predetermined temperature to be richer than that set after reaching the predetermined temperature, up cold start of the internal combustion engine.
However, since the invention disclosed in the above-identified Japanese Patent Application Laid-Open No. 11-294220 performs second injection immediately after starting up of the engine where temperatures of peripheral wall of the cylinder and a piston are low (after stopping a starter motor), fuel of the second injection injected toward the peripheral wall of the cylinder cannot be atomized sufficiently to degrade combustion to results in discharge of large amount of HC and CO. On the other hand, a technology disclosed in the above-identified Japanese Patent Application Laid-Open No. 11-311139 does not disclose a method of exhaust gas purification before the temperature of the catalytic converter does not reach a temperature of 200° C., at which HC is oxidized. When the catalytic converter is arranged below a floor panel, it takes a long period for rising the catalytic temperature to results in discharging of large amount of HC and CO to the atmosphere.